30 April 2009

There has been a proposal for several years now to build a new bridge across the Rhine in the Upper Middle Rhine Valley, between Mainz and Koblenz at the town of St Goarshausen. It has been deeply controversial, as this part of the valley was declared a World Heritage Site by UNESCO in 2002.

Near the bridge crossing is the Lorelei rock (pictured right, image courtesy of waterproof on Flickr), which is sometimes reputed to be the site where the treasure of the Nibelungen lies hidden. There are no bridges within an 80km length of the river, with crossing presently only possible by ferry.

An international bridge design competition has recently been organised, to find a bridge which is suitable for this historic location, with an estimated capital budget of 40m euros available. The contest featured some of the greatest bridge designers of recent decades: Christian Menn, Leonhardt Andrae und Partner, Wilkinson Eyre, Schlaich Bergermann, and others.

The winner has been announced as Arup with Heneghan Peng architects, the latter being perhaps best known in the bridges field for their London Olympic footbridge. Second place has been awarded to Ingenhoven Architekten, and third place to Schlaich Bergermann / Wilkinson Eyre. Prizes of 40,000, 32,000 and 18,000 euros were provided.

The winning design will now be presented to UNESCO in June, to seek their approval for this somewhat radical intervention in the Middle Rhine's picturesque landscape.

"The bridge proposal should demonstrate that there is no break of scale and materials of the future construction in comparison to the existing elements of the World Heritage property (castles, villages)."

The ICOMOS representative went further:

"It should be absolutely clear and there can be no doubt that any alterations such as the erection of a modern bridge in the core of the World Heritage site would ruin the outstanding universal values which are inseparably connected with the Romantic perception of this landscape."

ICOMOS is a non-governmental body with no authority over the World Heritage Site, so it might be expected that their more extreme view will be discounted in due course.

However, it's hard to see how any of the designs match the "scale" or "materials" of the local architecture, so it will be interesting to see what view UNESCO take in June.

The winning design seems somewhat self-conscious, an attempt to be radical for its own sake. The truss and box girder combination is unlikely to be especially efficient and it makes me wonder whether a box girder on its own would have been less visually intrusive.

The Ingenhoven design takes precisely that approach, and is my favourite of the three prizewinning designs. By contrast, the Schlaich Bergermann design is a gargantuan and unusual suspension bridge, which in the visualisations seems grossly out of scale to the surroundings. I suspect the images don't do it justice, as the cables could have far more potential to disappear into the background visually.

I also like the Knight Architects design - straightforward, slender, a less aggressively modern type of bridge. The Acme entry is admirably self-effacing and has the merit of considering the river-edge landscaping carefully (I gather this was a basic requirement of the competition) - but possibly too much so, as more minimal treatment of the landscape may have been preferred by the jury.

WinnerArup / Heneghan Peng

SecondIngenhoven Architekten

ThirdSchlaich Bergermann / Wilkinson Eyre

OthersI've only received images of two of the other entries - if anyone else would like to send their entry to happypontist at googlemail dot com, I'll include it here.

27 April 2009

After seeing threehistoricbridges in Scotland, it was time to finish off with something much more modern. So modern, in fact, that it hasn't yet reached its first birthday.

I posted about the £5m Harthill Footbridge when it was installed in October 2008. It spans 70m across the M8 Motorway, connecting the eastbound and westbound service stations at Harthill. It was designed by Buro Happold, adopting the same unusual helical form they had previously applied to Edinburgh's Greenside Place footbridge.

At Greenside Place the complex steel truss had (some) justification, as the bridge is S-shaped on plan and the helical truss is to some extent an efficient way of resisting the resulting torsion.

Nonetheless, it's a very expensive solution, as the cost of bending and welding together all the tubular elements must be well in excess of what is involved in a more conventional truss or box-girder solution. It also leads to a substantial amount of understressed metalwork, as the same cross-section appears visually to be applied throughout, although the various load effects in the bridge will vary considerably.

At Harthill Services station, these issues become more prominent, as the bridge is straight in plan and hence torsion is greatly reduced. The bridge's aesthetics also become far more problematic - a bridge looking like a tube can look okay when spanning between the vertical facades of buildings (see also Manchester's Corporation Street footbridge for an example). When sat with its ends in mid-air, it looks awkward.

The end termination problem is exacerbated by the very short cantilever end spans (I believe the spans are 10m, 70m, 10m) and the very differently styled approach ramps, which are there to provide disability access without the maintenance liability required by a lift. Personally, I think lift towers at either end would have looked far better. The new staircases are also somewhat cheap-looking compared to the rest of the bridge.

Of course, many of these issues are likely to be the result of choices outside the designer's control. The approach walkways, staircases and span arrangements will all be constrained both by the limitations of the site and of the client's budget. An attempt has been made to use interesting "trussed" parapets on the approach ramps to echo the diagonals of the main span elevation, but it just begs the question of why the main span isn't also a more straightforward Warren truss. Indeed, why is it covered at all, when there is a lengthy uncovered approach at either end?

The bridge is not without its attractions. The helical truss allows the main structure to be divorced from the glazed walkway enclosure, acting as a skeletal cradle, with an interesting visual rhythm (it will also make the outside of the glass a bugger to access for cleaning). It's also undoubtedly nice to see a major UK highways client investing in something aesthetically different and avoiding the identikit bridges which litter British motorways.

But for me, this was an interesting bridge to stop and see, but not one to love.

25 April 2009

Rumbling Bridge. It was just a dot on a map, but with a name like that it was a dot that just begged for a visit, especially after seeing two ShakkingBridges already on my trip to Scotland.

According to the internet, which is supposedly never wrong, the original Rumbling Bridge was built in 1713 by William Gray, carrying a road across the River Devon, at a point where it drops deep into a gorge, the water's rumbling sound giving the bridge its name. It's a masonry arch spanning about 7m, and without any parapets.

Again according to the internet, the second arch bridge was built above the original in 1816, leading to an unusual double arch bridge which is well worth seeing, particularly above the somewhat spectacular river gorge.

Quite how accurate or complete the internet's information is must be open to doubt, as there's a stone clearly visible on the bridge inscribed with the name "T.H. Tuckett" and dated 1664, which suggests there was a bridge on this site at an earlier date.

The photo at the start of this post is a panorama and hence slightly distorted and doesn't really give a good idea of the depth from the top of the bridge to the river below - it's deeper than it looks (36m). The old postcard on the left gives a slightly better idea and shows that at one time it was possible to walk across the lower arch - it's a real shame that's no longer an option.

It's unclear precisely why the lower arch bridge was left in place, as it must have been rendered largely unuseable during erection of the timber centering for the upper arch, and remains unuseable now. I did wonder briefly whether it formed some propping function, but that also seems unlikely.

Whatever, it's an unusual and picturesque bridge, worth the short detour from our journey.

23 April 2009

No that's not a typo, fresh from my visit to Aberdeen's Shakkin' Briggie, it was time to visit Edzell's similarly monickered Shakkin' Brig. Like the bridge over the River Dee, the Edzell bridge is a suspension footbridge, although it's not yet a ruin, and not particularly shaky, either.

It was apparently built in 1900, although I think little of the current structure is that old, and I gather that it was rebuilt in the mid-1990s by US servicemen. It crosses the North Esk river just east of the town, and can be found from a footpath behind the village post office.

Quite how much it has been altered is hard to identify: the image above right is from the 1970s (courtesy of RCAHMS), and it doesn't seem much different today. However, old postcards like the one on the left (date unknown) seem to show very different towers to those now present.

Structurally, it's Edzell's little equivalent of the Brooklyn Bridge, with a hybrid suspension and cable-stayed support system. You can just about make out the cable-stays on the image on the right. You can also see horizontal tie rods, which run from the midspan diagonally to the bank, and ensure that the Brig is not really very Shakky.

The tower-tops support a mess of cable rods heading off in what seems like several arbitrary directions. The anchorages are similarly higgledy-piggledy in their layout.

What I like about the Edzell bridge is the detailing. Like many rural bridges, the simple mesh parapets and chicken-wire anti-slip tread (shown right) are a cheap but effective solution which (sadly) slavish adherence to design standards rarely allows to spread more widely.

The eyelet connection between the hangers and the main cable chains, shown on the left, is similarly delightful in its simplicity (if clearly unsuitable for any more significant bridge).

The Shakkin' Brig at Edzell isn't a startling design, nor an especially historically significant structure. Its lack of Shakkiness is really rather disappointing.

But it's a fine example of robust vernacular construction (it would seem almost a shame to query who the designer was). It's also a good example of the continuing relevance of the suspension bridge form to relatively tiny spans (for other examples of similar historical vintage see the bridges of Louis Harper or David Rowell).

I'm told by ex-US Navy Seabee Robert Deese that the bridge was rebuilt in the mid-90s, by a four-man team, essentially replacing all the timber (which was rotten) with new pressure and chemically treated wood. So, the current design dates at least from before then. According to Robert:

"The rebuild was requested by the village because the bridge was unsafe. We supplied the labor at no charge and the village paid for the materials. The job was completed in 4 weeks right in the middle of winter. I had to take a swim twice to recover tools that dropped in the river. Man was that water cold!"

21 April 2009

I recently made a trip up and down the east coast of Scotland, and while looking for bridges was far from the purpose of the journey, I did visit one or two along the way.

These weren't necessarily spectacular structures in any way, indeed several were in varying states of dilapidation ranging from "senior citizen" to "six feet under". But they all had enough of interest to merit including them here.

The first bridge of interest was Aberdeen's Shakkin' Briggie, also called St Devenick's or Morison's Bridge. Built in 1837 on behalf of a local churchman, the bridge was designed by Aberdeen's city architect John Smith, who had worked six years previously with Captain Samuel Brown to design the Wellington Suspension Bridge, also in Aberdeen. The image on the right (courtesy of RCAHMS and dating from the mid-1970s; all B&W images are from the same source; all colour images are mine) shows the bridge a few decades ago and gives a fair idea of its original appearance.

The 55m span suspension footbridge originally provided access across the River Dee for over 700 churchgoers, and got its nickname from its somewhat flexible unstiffened deck.

The bridge was damaged several times by flooding, and affected by changes in the river channel, with its southern spans destroyed in 1955. In 1971, it was declared a Listed Building, but this offered it little protection as in 1984 it had deteriorated so badly that all the decking was removed. The image below right is from the mid-70s while it was in poor condition but still largely intact.

Its twin problems were that nobody knew who actually owned it, and that it was no longer part of a significant footpath route.

Today, it's a sad sight. As is often the case with historic bridges, it has been allowed to fall into ruin over the years to the extent that is probably now beyond repair.

Its Doric-style cast iron columns are heavily rust spotted, while the iron bar main cables and hangers are sufficiently rusty that it's surprising they haven't fallen into the river. Transoms connecting the hangers might suggest an unusual way across for an enterprising trapeze artist, at best.

There seems no hope of resuscitation from its current comatose state, but this elderly patient still endures. It sits silently, an accusation against municipal penny-pinching and lack of foresight. At any point, it could have been saved for the cost of medicinal repair far less than would now be required to give it renewed life.

If this were a ruined stately home, it would be given protection and funding by a body like Historic Scotland. Its Listed status might actually offer it some assistance. But the vision needed to create new riverside paths that might justify funding for refurbishment seems to have remained absent for a quarter of a century now.

It's hard not to assume that within the next quarter century, much of what now remains will end up at the bottom of the river.